I will add my 2 cents that anything on the road to/from JFK is risky. I live in central NJ near Princeton. In the early morning, with no traffic, I can make the trip in 75-80 minutes. Then I decided, for a noon flight to NRT, to allow 4 1/2 hours, "just in case". I made the flight by about 30 minutes. We spent two hours crawling thru Staten Island at 5 miles an hour, for no reason, other than volume. Then we crawled along the Beltway at 10 miles an hour. Its a good time to have some Maalox or Valium available. This trip is now to the point where it really is unpredictable. Coming from JFK, once you get out of NY and into NJ, it should be clear sailing to PHL.

For my last trip JKF-SYD, I took NJ transit to NY, then the A train to JFK for a total of about 2 hours and 15 minutes.

IMHO, the transit system is a lot more reliable than this kind of a drive.